This invention relates generally to energy storage systems, and more particularly, methods and apparatus for coupling an energy storage system to a variable energy supply system.
At least some known wind generation systems produce a fluctuating or intermittent power output due to the variability of wind speed. When multiple generators are electrically coupled together, i.e. in arrangements known as wind farms, the fluctuation in total power output may be reduced. Under ideal conditions the variations of power output will decrease at a factor of 1/√{square root over (n)}, where n represents the number of wind generators coupled together. In areas where wind penetration may be high, coupling a large number of generators generally reduces the overall power fluctuations on a system wide basis, but may still cause power swing stability concerns. Generally the volatile nature of wind generation output limits the amount of wind generation that can be connected to the grid without causing voltage stability problems. As such, wind power generation is generally considered a non-firm resource for system planning purposes.
It is well known that the demand for electric power fluctuates. Normally power fluctuations occur on a relatively regular basis. For example, in a typical residential electric power grid, generally demand for electric power is low at night, peaks during the morning, levels out during the day, and peaks again in the late afternoon. However, there are circumstances where the demand for electric power suddenly and irregularly increases. From the perspective of an electric power utility company, the associated increase in electric power demand occasioned during such occasions may be difficult to accommodate because the electric power demand are generally short lived.
For example, at least some known electric energy storage systems include banks of electric batteries. Known battery installations are used to provide electric power in emergency or power-failure circumstances, but generally can not be used to provide supplemental power during demand peaks. For example, known lead-acid batteries are used as standby power sources that may provide emergency lighting and/or standby power sources for telephone exchanges. However, such batteries either do not have adequate electric energy storage capacity to meet the demands of energy storage systems, or are expensive. To facilitate accommodating short lived electric power demand increases, at least some known electric power transmission system are coupled to electric energy storage system to an so that the energy storage system may be utilized, or turned on, to provide additional electric power during peak demand.